The present invention relates generally to trip units. More specifically, the present invention relates a method of error detection and correction in an electronic trip unit.
Electronic trip units are well known. Electronic trip units typically comprise voltage and current sensors which provide analog signals indicative of the power line signals. The analog signals are converted by an A/D (analog/digital) converter to digital signals which are processed by a microcontroller. The trip unit further includes RAM (random access memory), ROM (read only memory) and EEPROM (electronic erasable programmable read only memory) all of which interface with the microcontroller. Data, typically status of the circuit breaker, is displayed by a display. An output control circuit controls a trip module. Calibration, testing, programming and other features are accomplished through a communications I/O port. A power supply which is powered by the service electricity, provides appropriate power to the components of the trip unit.
The ROM includes trip unit application code, e.g., main functionality firmware, including initializing parameters, and boot code. The EEPROM contains operational parameters for the application code, e.g., encoded enumerations for parameters such as 50/60 Hz., UL/ANSI/IEC, etc. Operational parameters stored in EEPROM are generally stored as fixed or floating point values and enumerations. An operational parameter such as a calibration factor or "pickup" setpoint is generally stored in fixed or floating point, e.g., 1.5. Eunmerators are used for discrete operators, such as 50 Hz. vs 60 Hz. applications or UL vs. ANSI bs IEC protection "standard" selection. The integrity of the code is typically monitored using CRC (cyclic redundancy check) or checksum, as are well known. Corrupted data in the EEPROM is corrected by reading fail-safe default data from the ROM and over writing the default data into the EEPROM. This often results in less than optimal trip unit performance. For example, a trip unit intended for 60 Hz. operation may be defaulted to 50 Hz. Accordingly, a need exists for a method to accurately restore corrupted enumeration data in electronic trip units.